PR libstdc++/51798 * config/cpu/generic/atomicity_builtins/atomicity.h (__exchange_and_add, __atomic_add): Use __atomic_fetch_add with __ATOMIC_ACQ_REL semantics instead of __sync_fetch_and_add. * include/ext/atomicity.h (__exchange_and_add, __atomic_add): Likewise. From-SVN: r183644